Persistent developmental stuttering is a speech disorder that affects approximately 1% of the world's population and is easily recognizable by its hallmark characteristics of: whole-word repetitions, part-word repetitions, syllable prolongations, or the inability to get the sound or syllable out at all (inaudible postural fixations). While the symptoms of stuttering are well-known, the etiology is not. Without a clear understanding of what causes stuttering, the treatments for stuttering are limited. Consequently, there are no valid cures for the pathology, and the best available speech treatments of the prior art only allow for a limited amount of control over stuttered speech. Subsequently, the inability to successfully control (or eliminate) stuttering produces negative consequences of life-altering significance. In short, the inability to orally communicate in a socially acceptable fashion has the potential to drastically reduce professional, social and educational opportunities.
It has been shown that the incidence of stuttering can be reduced by using a second speech signal via speech feedback. Stuttering was reduced by having a stutterer speak in choral unison with another speaker. Technology allows us to mimic this effect, with Delayed Auditory Feedback (DAF) or Frequency Altered Feedback (FAF). The principles of DAF/FAF can be delineated into three simple stages: (1) a microphone captures the speaker's speech signal; (2) this speech signal is then digitally processed, where an adjustable delay is added to the signal (50 ms to 200 ms) and/or the frequencies in the speech signal are shifted higher or lower; (3) this altered speech signal is then re-introduced to the speaker via headphones. A variety of DAF/FAF devices are already on the market; however, they are expensive and distracting to use. These DAF/FAF devices suffer from many problems. For example, they have a poor signal to noise ratio. Additionally, the earphones interfere with hearing the surrounding environment. Visual speech feedback has also been shown to significantly enhance fluency via visual choral speech or delayed visual feedback; however, this methodology is not amenable to prosthetic implementation due to cost form and factor.
Treatments such as auditory feedback and visual feedback have proven to be effective but have the downside of being either audibly or visually distracting. Prosthetics based on these treatment methodologies are annoying to the user, they impede hearing and negatively affect dynamic conversation, and the signal to noise ratio is often almost unacceptably low. There exists a need for a method and device that can effectively reduce stuttering without the problems exhibited by the visual and auditory feedback methods.